1. Field of the Invention
The present invention relates to an extremely low or low frequency (ELF or LF) magnetic field distribution measuring system, which can achieve a good isotropy and a high spatial resolution by use of a small 3-axes magnetic field probe.
2. Description of the Related Art
As a well known fact, electricity has become an essential energy source for modern life. However, it became important to prepare appropriate measures to prevent electric and magnetic fields, if they are overwhelming, inevitably generated by the use of the electricity, from being inflicted possible harmful effects on the human body.
Generally, when being exposed to low frequency electric or magnetic fields, the human body experiences only a slight energy absorption and imperceptible body temperature increases. The major mechanism of the interaction by the outer field below 100 kHz is the induction of currents in the body. However, when being exposed to an electromagnetic field of approximately 100 kHz or more, the human body suffers body temperature increase by energy absorption. Generally, the human body experiences very inhomogeneous energy accumulation or field distribution if it is exposed to uniform electromagnetic fields. Thus, the energy accumulation or field distribution must be evaluated based on the measurement or calculation of the exposure.
Electromagnetic fields, generated from power transmission lines or household electrical appliances mainly have a frequency of 50 Hz or 60 Hz spectrum. Accordingly, there are many ongoing studies worldwide about the effect of ELF (extremely low frequency) frequencies of 50 Hz and 60 Hz, or LF (low frequency) magnetic fields on the human body.
Conventional probes for use in the measurement of ELF or LF magnetic fields, are designed to represent the sum of components for omnidirectional characteristic or designed for uniaxial measurement. In case of a single axis probe, it responds to only one field axis component. Thus, it is necessary to orient the probe orthogonally three times in order to obtain the correct magnitude of each vector. However, this sensing procedure is inconvenient to perform, time-consuming, and exhibits low measurement accuracy. If the magnitude of the field fluctuates as time, three orthogonal measurements can be almost meaningless.
However multiple axes sensors are used to sum up three components of a spatial field simultaneously. The multiple sensors are able to perform a measurement regardless of the polarization or direction of the existing field components. In this case, there is the need of a small isotropic probe having three axes arranged perpendicular to each other. The small isotropic probe ensures that root-sum-square (rss) values of the measured field are constant regardless of the direction of a magnetic field vector.
For the space resolution of the measurement, the probe is configured in IEC 62233 (2002) to have a cross sectional area of less than 0.01 m2. However, with such a great cross sectional area of the conventional low frequency 3-axes probe, it is not possible when the probe should be located excessively close to a field source. As a result, using the conventional low frequency 3-axes probe it is difficult to measure a near field having a very steep rate of spatial change and it exhibits only a very low spatial resolution.